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Spectrum scarcity is one of the most important challenges in wireless communications networks due to the sky-rocketing growth of multimedia applications. As the latest member of the multiple access family, non-orthogonal multiple access (NOMA) has been recently proposed for 3GPP Long Term Evolution (LTE) and envisioned to be a key component of the 5th generation (5G) mobile networks for its potential ability on spectrum enhancement. The feature of NOMA is to serve multiple users at the same time/frequency/code, but with di erent power levels, which yields a signi cant spectral e ciency gain over conventional orthogonal multiple access (OMA). This thesis provides a systematic treatment of this newly emerging technology, from the basic principles of NOMA, to its combination with simultaneously information and wireless power transfer (SWIPT) technology, to apply in cognitive radio (CR) networks and Heterogeneous networks (HetNets), as well as enhancing the physical layer security and addressing the fairness issue. First, this thesis examines the application of SWIPT to NOMA networks with spatially randomly located users. A new cooperative SWIPT NOMA protocol is proposed, in which near NOMA users that are close to the source act as energy harvesting relays in the aid of far NOMA users. Three user selection schemes are proposed to investigate the e ect of locations on the performance. Besides the closed-form expressions in terms of outage probability and throughput, the diversity gain of the considered networks is determined. Second, when considering NOMA in CR networks, stochastic geometry tools are used to evaluate the outage performance of the considered network. New closed-form expressions are derived for the outage probability. Diversity order of NOMA users has been analyzed based on the derived outage probability, which reveals important design insights regarding the interplay between two power constraints scenarios. Third, a new promising transmission framework is proposed, in which massive multipleinput multiple-output (MIMO) is employed in macro cells and NOMA is adopted in small cells. For maximizing the biased average received power at mobile users, a massive MIMO and NOMA based user association scheme is developed. Analytical expressions for the spectrum e ciency of each tier are derived using stochastic geometry. It is con rmed that NOMA is capable of enhancing the spectrum e ciency of the network compared to the OMA based HetNets. Fourth, this thesis investigates the physical layer security of NOMA in large-scale networks with invoking stochastic geometry. Both single-antenna and multiple-antenna aided transmission scenarios are considered, where the base station (BS) communicates with randomly distributed NOMA users. In addition to the derived exact analytical expressions for each scenario, some important insights such as secrecy diversity order and large antenna array property are obtained by carrying the asymptotic analysis. Fifth and last, the fundamental issues of fairness surrounding the joint power allocation and dynamic user clustering are addressed in MIMO-NOMA systems in this thesis. A two-step optimization approach is proposed to solve the formulated problem. Three e cient suboptimal algorithms are proposed to reduce the computational complexity. To further improve the performance of the worst user in each cluster, power allocation coe cients are optimized by using bi-section search. Important insights are concluded from the generated simulate results.

Cognitive radio (CR) is one of the most prominent technique to deal with the radio spectrum scarcity problem. CR systems can improve radio spectrum utilization by opportunistically accessing the underutilized spectrum resource of the licensed users. In interweave implementation, the secondary user (SU) has to wait and locate spectrum holes before its transmission. Therefore, the extended delivery time (EDT) for the secondary user consist of both wait slots and transmission slots. We study the EDT analysis of fixed size secondary packet transmission over multiple primary channel. In particular, we introduce a birth-death based approach to model the cognitive transmission of the secondary user over multiple primary channels. We use this approach to derive the exact probability density function and probability mass function of EDT of the secondary transmission for both continuous and periodic sensing cases. We also present selected numerical and simulation results to verify our analytical approach and to illustrate the mathematical formulation. / Graduate

本文取徑經濟學的公共財概念，試圖從此一角度出發探討頻譜管理從「稀有論」轉向「公有論」的論述正當性，並釐清管理模式與財貨特性之關連。根據研究結果，頻譜資源的原始狀態雖符合公共財定義，但並非任何人所有，其財貨特性會隨著科技發展和法律制度而變動，因此「頻譜公有」的論述並未獲得專家學者支持。 儘管如此，頻譜資源在運用上需避免使用者相互干擾，因此建立一套合理的使用秩序，方能促使資源發揮效用。針對提供商業服務之頻譜，本文建議主管機關在規劃與指配上應給予使用者更多彈性，以類似出租國有地的方式，視頻譜資源為獨立客體並制訂相關法律；其次為放寬技術與用途限制，並在釋出資源後開放頻譜二次交易，讓分配效率得以提升。 長期而言，無線通訊科技將不斷演化，當干擾問題可獲得妥善解決，為追求資源使用效率，本文建議管理模式應朝開放共享的方向邁進。簡言之，「頻譜管理」任務本身就是一種公共服務，政府責無旁貸，唯有充分掌握頻譜資源的供給與需求變化，施政方針才能充分反應使用者需求。 / This research argues that the scarcity rationale could be replaced by public spectrum rationale. The research results show that although the nature of spectrum resource is public good by economic definition, it doesn’t mean the resources are owned by the public. Therefore, the ownership of resources should be clearly defined under the law to prevent users from interfering with each other. For spectrum used in private sector, the allocative efficiency is important for some valuable blocks of spectrum such as 800MHz, 900MHz, 1800MHz, 2600MHz. To improve allocative efficiency, the research result suggest that the government could legislate specific laws on spectrum management, while allowing users to decide how they want to make use of the resources. In the long run, wireless communication technology will keep developing. As long as signal interference can be controlled under specific conditions, spectrum sharing including common regime and license-exempt use should be adopted. A government plays the key role which not only provides management service but should also have a systematic plan for improving spectrum efficiency.